Panoramic elasticity ultrasound imaging

ABSTRACT

Using compression, tissue elasticity data from two or more different fields of view are acquired. Since different amounts of compression may be used for the different fields of view, the dynamic range of the elasticity data is updated. A panoramic elasticity image is generated from the updated elasticity data of multiple fields of view. A panoramic elasticity image represents the combined fields of view for the elasticity data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/237,204, filed Sep. 27, 2005, now U.S. Pat. No. 7,678,051.

BACKGROUND

The present embodiments relates to panoramic ultrasound imaging.Panoramic images are generated for B-mode and Doppler information. U.S.Pat. Nos. 5,782,766, 6, 5,910,114, 6,503,201, 6,572,549, 6,730,031, and6,641,536 describe some methods to generate panoramic images. Relativemotion between adjacent frames is detected. The frames are assembledbased on the relative motion into an extended field of view.

Another ultrasound imaging mode is elasticity imaging. U.S. Pat. Nos.5,107,837, 5,293,870, 5,178,147, and 6,508,768 describe methods togenerate elasticity images using the relative tissue displacementbetween adjacent frames. Strain, strain rate, modulus, or otherparameters corresponding to tissue displacement are detected forgenerating an elasticity image. U.S. Pat. No. 6,558,324 describesmethods to represent elasticity using color coding.

BRIEF SUMMARY

By way of introduction, the preferred embodiments described belowinclude methods, instructions and systems for panoramic elasticityimaging. Using tissue compression, elasticity data from two or moredifferent fields of view is acquired. Since different amounts ofcompression may be used for the different fields of view, the dynamicrange of the elasticity data is updated. A panoramic elasticity imagerepresents the combined fields of view for the elasticity data.

In a first aspect, a method is provided for elasticity ultrasoundimaging. First elasticity data is acquired with ultrasound for a firstregion corresponding to a first position of a transducer. Secondelasticity data is acquired with ultrasound for a second regioncorresponding to a second position of the transducer. The secondposition and second region are different from the first position andfirst region, respectively. An image represents both the first andsecond regions. The image is generated a function of the first andsecond elasticity data.

In a second aspect, a computer readable storage medium has storedtherein data representing instructions executable by a programmedprocessor for extended field of view ultrasound imaging. Theinstructions are for generating a panoramic tissue elasticity image.

In a third aspect, a method is provided for extended field of viewultrasound imaging with elasticity or other types of data, such asB-mode. Relative displacement between frames of data is determined. Forexample, a primary displacement is determined by correlation between twoor more frames. The primary displacement is decomposed into first(lateral direction) and second (axial direction) displacements. If thefirst displacement is greater than the second displacement, the two ormore frames are combined as a function of the primary displacement. Analternative implementation is to separately compute the mean correlationin first direction, namely first correlation, and compute the meancorrelation in second direction different from the first direction,namely second correlation. A displacement is chosen in the firstdirection and two or more frames are combined as a function of the firstdirection if the first correlation is greater than the secondcorrelation.

The present invention is defined by the following claims, and nothing inthis section should be taken as a limitation on those claims. Furtheraspects and advantages of the invention are discussed below inconjunction with the preferred embodiments and may be later claimedindependently or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

The components and the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.Moreover, in the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a flow chart diagram of one embodiment of a method forpanoramic elasticity imaging;

FIG. 2 is a representation of a panoramic elasticity image and twocomponent frames;

FIG. 3 is a graphical representation of updating the dynamic range ofcomponent frames of data for panoramic display; and

FIG. 4 is a block diagram of one embodiment of a system for panoramicelasticity imaging.

DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED EMBODIMENTS

An extended field of view is provided for elasticity imaging. Thispanoramic elasticity image may be useful in clinical practice. Sincedifferent frames of elasticity data have different dynamic range due tovariation in compression, the elasticity data for each frame may benormalized, minimizing frame-to-frame artifacts in the panoramic image.Since elasticity may be determined from radio frequency data orpre-detection data, the alignment of the frames of data may also bebased on radio frequency data. Since elasticity is based on compressionor tissue displacement, motion related to extending the field of viewmay be distinguished from motion related to elasticity imaging. Eitherreal-time or off-line generation is provided.

FIG. 1 shows a method for extended field of view ultrasound imaging.Some of the acts may be used for extended field of view B-mode or othermodalities of imaging. For example, pre-detection data based alignmentor distinguishing between types of motion may be used. In someembodiments, the method is for elasticity ultrasound imaging orgenerating a panoramic tissue elasticity image. Additional, different orfewer acts may be provided. For example, an elasticity panoramicultrasound image is generated without generating a B-mode image in act26 or a panoramic B-mode image in act 28. As another example, thedisplay or archiving act 30 is optional. As another example, theelasticity panoramic image generated in act 24 or the associatedsupporting acts 16, 18 and 20 are not performed. The acts are performedin the order described or shown, but other orders may be provided.

In act 12, radio frequency data is received. The data is responsive toultrasound transmissions and echoes. The radio frequency data isbeamformed or represents different spatial locations scanned withultrasound. For generation of a two or three-dimensional panoramicimage, the data corresponds to two or more scans of overlapping butdifferent regions. For example, FIG. 2 shows two component frames ofdata 42, 44 in panoramic fields of view 41 displayed as an image 40.More than two frames of data may be acquired. FIG. 2 shows the panoramicfield of view 41 generated from ten or more frames of data. Frames ofdata represent two or three dimensional regions or scans, such asassociated with a complete scan or the transducer being generally at asame location. For three-dimensional imaging, a plurality oftwo-dimensional scans may represent the volume. The volume is extendedby moving the transducer and scanning the next volume for compositingwith the first volume.

The panoramic image 41 is generated from two or more frames ofelasticity data representing overlapping but different regions. Theelasticity data is information used to estimate stiffness of tissue,such as strain. The data is responsive to compression force or otherstress applied to the tissue being scanned. For example, a user appliespressure axially while maintaining a transducer at a lateral location orwhile translating the transducer laterally. Ultrasound scanning isperformed while applying pressure with the transducer against thepatient. Alternatively, another source of stress or compression is used,such as acoustic energy or movement within the body.

Where compression force is applied by the transducer, the data forelasticity imaging may be acquired while generally maintaining a lateralposition of the transducer, but lateral movement may occur. Axialcompression is applied while the ultrasound data is acquired. Uponcompletion of one or more scans, the transducer is moved from oneposition to another position. The movement allows for overlapping scanregions, but non-overlapping fields of view may be provided. Themovement is manual or by the user, but guided or automated movement maybe provided. Referring to FIG. 2, each frame of data 42, 44 represents adifferent region corresponding to different transducer positions. Aftermoving to the other position, elasticity data is acquired for thecurrent position. Ultrasound scanning is performed again while applyingpressure with the transducer against the patient while the transducer ismaintained in the current position. This process ends after scanning tworegions or may continue for scanning three or more regions.

In act 14, a displacement between frames of data is determined. Thedisplacement is determined along one, two or three dimensions with orwithout rotation in one, two or three dimensions. FIG. 2 shows one frameof data translated laterally and axially as well as being rotated withinthe plane of the figure. In one embodiment, the displacement isdetermined from sensors, such as a magnetic position sensor on thetransducer.

In another embodiment, the displacement is determined from ultrasounddata. Speckle or features of the patient being scanned may be tracked.For example, an alignment is determined from elasticity data. As anotherexample, the alignment is determined from B-mode or Doppler data. Asanother example, the radio frequency data or pre-detected data is usedto determine the alignment. Pre-detected data may provide more accurateinformation for the motion vector between frames of data. The alignmentprovides relative positioning of the frames of data for generating thepanoramic image. Any now known or later developed technique forestimating the motion vector or determining the displacement betweenframes or data may be used, such as any one or more of the techniquesdisclosed in U.S. Pat. Nos. 5,782,766, 6, 5,910,114, 6,503,201,6,572,549, 6,730,031, and 6,641,536, the disclosures of which areincorporated herein by reference.

In act 16, the displacement or motion vector is decomposed. A processordistinguishes between moving the transducer in a general lateraldirection between different positions and moving the transducer in ageneral axial direction for acquiring the elasticity data. The generallateral direction corresponds to translation to create the panoramicfield of view, and the general axial direction corresponds to thecompression force for elasticity imaging. Where the transducer ismaintained in a substantially same lateral position for elasticityimaging, then moved to extend the view, and then again maintained in asame position, the processor distinguishes between these events. In analternative embodiment, the user indicates whether the motion is forimaging or extending the field of view, such as by depressing a buttonor moving a switch.

In one embodiment, the motion is decomposed into lateral and axialcomponents of the motion vector. A primary displacement between two ormore frames of data is determined. The primary displacement isdecomposed into lateral and axial displacements. Other directions may beused, such as two or more directions which are not orthogonal orperpendicular to each other.

In another embodiment, direction correlations are computed. Correlationsinclude sum of absolute differences, correlation coefficients or othermeasures of similarity. The correlation along the different directionsis determined. For example, data from two or more frames of data iscorrelated along a plurality of parallel lines or one dimensionally. Anaverage, mean or other statistic of the directional correlation betweenthe two frames of data is determined.

The directional correlations are compared or used separately. Forexample, the process continues to act 18 for generation of elasticityimaging if the correlation along the axial axis is larger than thecorrelation along the lateral axis. The process continues to act 22 fordefining the extended field of view if the correlation along the lateralaxis is larger than the correlation along the axial axis. As anotherexample, the directional correlations are both used, but for thedifferent acts 18, 22. As another example, the axial motion orcorrelation is used for generating elasticity data in act 18 and bothaxial and lateral motion are used for defining the extended field ofview in act 22. One, two or three-dimensional motion may be used forelasticity or extended field of view. The same or different motions areprovided for the different acts.

In act 18, axial motion is used to generate elasticity data, such as aframe of data representing the elasticity of tissue. Elasticity orelastography are general terms that include various types of parametricimages of tissue stiffness, such as strain, strain rate, modulus orrelaxation, and various methods of mechanically generating them. Strainimages show tissue relative stiffness and deformation. Strain rateimages display the first time derivative of the strain. Local strainrate may indicate cardiac muscle contractility from which is inferredthe muscle health and condition. Modulus images (e.g., Young's modulus)may be generated when the strain image or strain rate image isnormalized by and combined with stress measurements. One method is tomeasure the pressure at the body surface with sensors attached to thetransducer. The stress field pattern is then extrapolated internally tothe points (i.e., pixels or voxels) of measured strain. Young's modulusis defined as stress divide by strain. Local modulus values may becalculated and those numerical values are converted to gray scale orcolor values for display. In strain imaging, local 1D, 2D, or 3Ddisplacements are measured and the numerical displacement values areconverted to gray scale or color values for display.

Strain images may be generated with manual palpation, external vibrationsources, inherent tissues motion (e.g., motion due to cardiacpulsations, or breathing) or acoustic radiation force imaging (ARFI).ARFI produces strain images or produces relaxation images. Relaxationimages may be displayed parametrically in similar fashion to strain andmodulus images. The parametric images are generated with one (e.g.,M-mode), two (e.g., B-mode), three (e.g., static volumetric), or four(e.g., dynamic volumetric) dimensional acquisition and imaging. In oneembodiment, any one or more of the methods or systems disclosed in U.S.Pat. No. 5,107,837, 5,293,870, 5,178,147, 6,508,768 or 6,558,324, thedisclosures of which are incorporated herein by reference, are used togenerate elasticity frames of data or images.

In act 20, the dynamic range of the elasticity data is updated to avoidframe-based artifacts in the panoramic elasticity image 41. Each frameof elasticity data may be a result of different compressions, changes incompression or other elasticity parameters. The upper and lower graphson the left of FIG. 3 show lines of data representing a same region butwith different amplitudes. The different amplitudes result fromdifferent amounts of compression being applied when acquiring the data.For the same tissue profile, two strain profiles generated under twodifferent compression force changes result in different dynamic ranges.Since strain is a relative value, its number may not give easily useddiagnosis information without knowing the stress.

To overcome the implicit drawback of the strain imaging, the dynamicrange of the elasticity data is updated. In most elasticity imagingapplications, the field of view of each strain image includes normalsoft tissue, such as breast fat tissue, that can be used as thereference. The normal softest tissue has the highest strain in the fieldof view as compared with other normal and pathological tissue. Accordingto Hook's law, the strain is linearly proportional to the stress. Thislinear relationship is valid when the compression is small. Thecompression is small in practical applications for ultrasound. The ratioof the strain in different tissues as a metric holds relatively constantalthough the strain values may vary under different compression force.

To update the dynamic range, each frame of elasticity data is normalizedusing the highest strain value from the frame of data. Alternatively,the normalization uses the elasticity data from the extended field ofview to determine a normalization value. For example, the maximum valueof strain is E_(max). For each pixel (x,y), a strain e(x,y) isdetermined. p(x,y) is the percentage calculated as e(x,y) divided byE_(max). The color-coding or data used for imaging is based on thepercentage value p(x,y), and the range of the color-coding is [α,1]. Thepercentage is mapped between α and 1. A value of 1 is the normal andmost transparent in color, and a value of α is the most hard and red incolor. The value α may be determined empirically from a set ofpathological data. FIG. 3 shows normalization or updating the dynamicrange as a cross reference metric map.

After normalization, each frame of data has a similar dynamic range. Inact 24, a panoramic elasticity image is generated as a function of thenormalized elasticity frames of data. In act 22, the extended field ofview parameters and control are generated. The parameters includedetermining the alignment or overlap from the displacement. The controldetermines whether overlapping data is discarded or combined withprevious data. Filter parameters for combination may be selected. Datarepresenting newly scanned spatial locations is identified and assignedto the appropriate locations on the extended field of view image. Wherethe dynamic range processing of act 20 is performed as a function ofdata selected for the extended field of view image or other extendedfield of view parameters, the information is used in act 20. Anotherparameter includes mapping or combination selection for the elasticityand other types of data. For example, a color map is selected forelasticity data and a gray scale map is selected for B-mode data. Acommon map outputting display values for a linear or nonlinearcombination of elasticity and other data may be provided.

Whether to display the elasticity data may also be controlled in act 22.Out of plane or rapid axial or lateral movement may result in incorrectelasticity estimation. In a real-time or live scan, the user may movethe transducer from place to place while investigating the region ofinterest. When the movement occurs, the resulting elasticitymeasurements may be noise that covers much or the entire associatedimage. To suppress noise, flash suppression is used. In one embodiment,the noise suppression is based on an amount of decorrelation betweenframes of data. The decorrelation is measured as the directioncorrelation from one or more directions used in act 16, or a differentcorrelation, such as a multidimensional correlation between two or moreframes of data. In one embodiment, localized correlation is determined,such as determining a correlation for each or a sub-set of the pixel orvoxel locations. A global or general correlation is determined from thelocal correlations. A mean or variance of correlation from the localizedcorrelations is calculated. For example, a first or second moment from ahistogram of the correlations indicates mean and variance, respectively.A map for the image or image values are selected as a function of theamount of correlation. If the correlation is above a threshold value,the elasticity data is used. If the correlation is below a thresholdvalue, B-mode data is used without elasticity data. Multiple levels ofthresholds may be used, such as varying amounts of emphasis ofelasticity data relative to B-mode data. The threshold may adapt, suchas changing in value based on the imaging application or ultrasounddata.

In act 24, an image representing two or more different regions of thepatient is generated. The image is a panoramic elasticity image. Theelasticity data is mapped to display values. Panoramic imaging is thegeneration of fields of view larger than a single image by correlatingsuccessive 2D images or 3D volumes and combining them into one compositedisplay. Panoramic imaging may more likely place local tissue lesionsand features into overall anatomical context and more likely providereference for surgeons, referring physicians, the patient, or the laypublic. As a continuing sequence of elasticity frames of data andassociated regions are obtained or provided, the extended field of viewimage is extended. Alternatively, the image is not displayed untilcomplete.

The panoramic elasticity image is displayed alone. Alternatively, aB-mode or other image representing the same extended field of view or adifferent field of view is displayed adjacent to the panoramicelasticity image. In another alternative embodiment, the elasticityimage is combined with or overlaid on the B-mode image.

In act 26, the same or different radio frequency data from act 12 isdetected. B-mode intensities are detected, but other imaging modes maybe used. The B-mode data may be used for determining extended field ofview parameters or control. In act 28, a panoramic B-mode image isgenerated.

In act 30, the panoramic tissue elasticity image is displayed or stored.For storage, elasticity data other than display values may be stored.Similarly, B-mode or other imaging data is displayed or stored.Component frames of data used to form the extended field of view may bealternatively or additionally stored.

FIG. 4 shows one embodiment of a system for speckle adaptive medicalimage processing. The system implements the method of FIG. 1 or othermethods. The system includes a processor 50, a memory 52, and a display54. Additional, different or fewer components may be provided. Forexample, a user input is provided for manual or assisted selection ofextended field of view parameters or other control. As another example,the system is a medical diagnostic ultrasound imaging system that alsoincludes a beamformer and a transducer for real-time acquisition andimaging. Other medical imaging systems may be used. In anotherembodiment, the system 60 is a personal computer, workstation, PACSstation or other arrangement at a same location or distributed over anetwork for real-time or post acquisition imaging.

The processor 50 is a control processor, general processor, digitalsignal processor, application specific integrated circuit, fieldprogrammable gate array, network, server, group of processors, datapath, combinations thereof or other now known or later developed devicefor estimating elasticity, determining extended field of viewparameters, identifying motion vectors, updating dynamic range,decomposing motion vectors or other acts. For example, the processor 50or a data path of processors including the processor 50 detects B-modedata, generating B-mode images and generates an extended field of viewB-mode image. As another example, the processor 50 or a data pathincluding the processor 50 performs any combination of one or more ofthe acts shown in FIG. 1.

The processor 50 operates pursuant to instructions stored in the memory52 or another memory. The processor 50 is programmed for extended fieldof view ultrasound imaging, such as programmed to generate a panoramictissue elasticity image.

The memory 52 is a computer readable storage media. The instructions forimplementing the processes, methods and/or techniques discussed aboveare provided on the computer-readable storage media or memories, such asa cache, buffer, RAM, removable media, hard drive or other computerreadable storage media. Computer readable storage media include varioustypes of volatile and nonvolatile storage media. The functions, acts ortasks illustrated in the figures or described herein are executed inresponse to one or more sets of instructions stored in or on computerreadable storage media. The functions, acts or tasks are independent ofthe particular type of instructions set, storage media, processor orprocessing strategy and may be performed by software, hardware,integrated circuits, filmware, micro code and the like, operating aloneor in combination. Likewise, processing strategies may includemultiprocessing, multitasking, parallel processing and the like. In oneembodiment, the instructions are stored on a removable media device forreading by local or remote systems. In other embodiments, theinstructions are stored in a remote location for transfer through acomputer network or over telephone lines. In yet other embodiments, theinstructions are stored within a given computer, CPU, GPU or system.

The memory 62 may store alternatively or additionally ultrasound datafor generating images. The ultrasound data is the radio frequency data,elasticity data or B-mode data, but may include alternatively oradditionally data at different stages of processing.

The display 54 is a CRT, LCD, projector, plasma, or other display fordisplaying two-dimensional panoramic images, or three orfour-dimensional panoramic representations.

While the invention has been described above by reference to variousembodiments, it should be understood that many changes and modificationscan be made without departing from the scope of the invention. It istherefore intended that the foregoing detailed description be regardedas illustrative rather than limiting, and that it be understood that itis the following claims, including all equivalents, that are intended todefine the spirit and scope of this invention.

We claim:
 1. In a non-transitory computer readable storage medium havingstored therein data representing instructions executable by a programmedprocessor for extended field of view ultrasound imaging, the storagemedium comprising instructions for: generating a panoramic elasticityimage from two or more frames of elasticity data acquired with atransducer placed at two or more different positions, the elasticitydata acquired in response to compression force at the two or moredifferent positions, each of the frames of elasticity data representingoverlapping but different regions, the different regions being laterallyoffset from each other, each of the frames of elasticity datarepresenting elasticity of tissue in the respective region,distinguishing between moving the transducer in a lateral direction frommoving the transducer in an axial direction, the lateral directioncorresponding to a panoramic field of view for the panoramic elasticityimage and the axial direction corresponding to the compression force,determining an amount of correlation between frames of data bydetermining a mean or variance of correlation between the frames ofdata, and selecting a map for the panoramic elasticity image by mappingelasticity data where the amount of correlation is above a threshold andmapping B-mode data where the amount of correlation is below thethreshold.
 2. The non-transitory computer readable storage medium ofclaim 1, wherein distinguishing comprises: determining a firstcorrelation between two or more frames of data in the general lateraldirection; determining a second correlation between the two or moreframes of data in the general axial direction; comparing the firstcorrelation to the second correlation; combining the two or more framesin an extended field of view when the comparing indicates that the firstcorrelation is greater than the second correlation; and generatingelasticity data when the comparing indicates that the second correlationis greater than the first correlation.
 3. The non-transitory computerreadable storage medium of claim 1 wherein generating comprisesdetermining an alignment as a function of B-mode data, and generatingthe panoramic elasticity image as a function of the alignment.
 4. Thenon-transitory computer readable storage medium of claim 1 whereingenerating comprises determining an alignment as a function ofpre-detected data, and generating the panoramic elasticity image as afunction of the alignment.